1. Field of Invention
The present invention relates to low bulk density thermoplastic polymers and more particularly it relates to fine particle size water-soluble synthetic or semisynthetic associative thickeners having low bulk density.
2. Description of the Prior Art
In general, the bulk density of polymer particles is lowered for ease of processing, handling and flow. In many situations, it is desirable to temporarily suspend polymer particles in a liquid medium for ease of handling and transportation. One of the ways to achieve this goal is to lower the bulk density of the polymer particles. In addition, by lowering bulk density, dissolution of polymer particles in an appropriate solvent can be accelarated. Low bulk density polymer particles are of special interest for fabricating light-weight products and separating solvents.
Various water-soluble polymers are used to thicken and control rheology of waterborne industrial systems, such as latex paints and personal care products. These include natural and chemically modified polysaccharides, proteins and synthetic water-soluble polymers. Examples include hydroxyethylcellulose (HEC), hydrophobically modified hydroxyethylcellulose (HM-HEC), ethylhydroxyethylcellulose, hydrophobically modified ethylhydroxyethylcellulose, methylhydroxypropylcellulose, carboxymethylcellulose, guar and guar derivatives, starch and starch derivatives, casein, polyacrylates, polyacrylamides, and polyalkylene oxides.
In the last fifteen years, a new class of hydrophobically modified synthetic water-soluble polymers (HM-WSPs) have gained extensive commercial importance for formulating waterborne coatings and suspensions to achieve desired paint properties, such as flow, leveling, film build and gloss. These HM-WSPs are composed of water-soluble and water-insoluble components. They are dubbed xe2x80x9cassociative thickenersxe2x80x9d as they thicken aqueous systems by intermolecular hydrophobic associations and/or hydrophobic associations between their hydrophobic moieties and other hydrophobic entities present in the system. Various types of synthetic associative thickeners (SATs) include, but are not limited to, hydrophobically modified polyether-polyurethanes (U.S. Pat. Nos. 4,079,028, 4,155,892, 4,496,708, 4,426,485, 4,499,233, 5,023,309 and 5,281,654), hydrophobically modified polyether-polyurethanes bearing terminal hydrophilic groups (PCT International WO 96/40820), hydrophobically modified polyether-polyols (U.S. Pat. Nos. 4,288,639, 4,354,956, 4,904,466), copolymers of ethylene oxide and long chain epoxyalkane (U.S. Pat. No. 4,304,902), hydrophobically modified polyacetal-polyethers (U.S. Pat. No. 5,574,127 ), hydrophobically modified alkali-soluble emulsions (U.S. Pat. Nos. 4,514,552, 4,421,902, 4,423,199, 4,429,097, 4,663,385, 4,008,202, 4,384,096, 5,342,883). For other references on hydrophobically modified alkali-soluble emulsions see, xe2x80x9cE. J. Schaller and P. R. Perry, in xe2x80x9cHandbook of Coatings Additivesxe2x80x9d, Ed., L. J. Calbo, Marcel Dekker, Inc., New York, Vol. 2, 1992, Chapter 4, p. 114 and G. D. Shay in xe2x80x9cPolymers in Aqueous Mediaxe2x80x9d, Ed. J. E. Glass, Advances in Chemistry Series, Vol. 223, Chapter 25, p. 480, 1989; American Chemical Society, Washington, D.C.), hydrophobically modified polyacrylamide (U.S. Pat. Nos.4,425,469, 4,432,881, 4,463,151, 4,463,152, 4,722,962), hydrophobically modified aminoplast-polyethers (PCT International WO 96/40625 and WO 96/40185).
To thicken aqueous systems, water-soluble polymers are commonly used in dry powder form. However, there are several problems associated with the use of dry powder polymers. These include, dusting during transfer, poor dispersibility (lump formation), unusually long dissolution time, and poor handling. Particularly, complete dissolution of solid water-soluble polymers is a formidable task when they are directly added to highly filled systems, such as latex paints, containing limited amount of free water.
To eliminate these problems, manufacturers of SATs have searched for means to deliver these polymers as high solids pourable/pumpable aqueous emulsions or solutions.
One class of SATs comprised of hydrophobically modified alkali-soluble polyacrylates and hydrophobically modified polyacrylamides are made by free radical emulsion polymerization processses in water and the polymers formed remained as stable colloidal dispersions. Hence, they are currently sold as 20-50% solids dispersions. At the point of applications, these dispersions are directly added to the aqueous system to be thickened and the polymer dissolved in water by exposing them to an alkali or a base. Alternatively, they can be first dissolved in water by adding an alkali or a base and the resulting polymer solution can be added to the aqueous system to be thickened.
Another class of important SATs is based on copolymers of polyalkylene oxides and other appropriate functional reagents. These polyalkylene oxide based SATs are made by step growth copolymerization processes and are widely used in a multitude of industrial applications. Examples of such commercial SATs include hydrophobically modified polyether-polyurethanes (sold under the trademark Acrysol(copyright) RM-825 and RM-1020 by Rohm and Haas Company and Rheolate 244, 255 and 278 by Rheox, Inc.) and hydrophobically modified polyether-polyols (sold under the trademark RHEOLATE(copyright) 300 by Rheox, Inc.). Currently these SATs are sold as 20-30% solids solution in a mixture of water and a water miscible organic solvent, such as diethylene glycol monobutyl ether (also known as Butyl carbitol(trademark)) or ethylene glycol or propylene glycol. The organic cosolvents are used to suppress the solution viscosity of SATs so that they can be delivered as high solids pourable/pumpable solutions.
While these organic solvents do provide the intended function, they eventually get released to the atmosphere and contribute to environmental pollution. Due to recent changes in environmental regulations in the United States, Western Europe and other parts of the world, there is a mounting pressure to formulate waterborne systems, such as latex paints, free of volatile organic compounds (VOCs). Since the above-mentioned polyalkylene oxide based SATs are dissolved in a mixture of water and an organic cosolvent, they are not the systems of choice for formulating VOC free waterborne coatings. Hence, manufacturers of SATs have been actively seeking for ways to deliver SATs in aqueous systems free of VOCs.
U.S. Pat. Nos. 5,137,571 and 5,376,709 describe the use of cyclodextrins to suppress the solution viscosity of SATs. It has been proposed that cyclodextrins, which are cyclic oligosaccharides composed of 6, 7 or 8 xcex1-D-anhydroglucose units, reversibly complex with the hydrophobic moieties of SATs and occasion breakdown of hydrophobic association and attendant viscosity loss.
A recent patent (U.S. Pat. No. 5,425,806), issued to Rheox, Inc., describes the use of an anionic or a nonionic surfactant to lower the solution viscosity of SATs and reduce the VOC of the thickening composition.
Although cyclodextrins and surfactants can suppress the aqueous solution viscosity of SATs, they can severely restrict the coating formulator""s ability to formulate paints. This restriction could arise due to the fact that the ingredients (latex binders, pigments, extenders, surfactants, and dispersants) of VOC free waterborne coatings can interact with cyclodextrins and surfactants to occasion instability to the paint and detract from achieving the target paint properties. For example, the presence of additional surfactants or cyclodextrins arising from the thickener solution can negatively impact the viscosifying ability of the SAT and can cause excessive foaming during the manufacture of the coating. Certain latex film properties, such as early blister resistance, block resistance, water resistance, and scrub resistance could also be adversely affected by incorporation of an excess of cyclodextrins or surfactants. In addition, cyclodextrins are fairly expensive and not cost effective based on their recommended use levels for making pumpable aqueous solutions of SATs.
Hence, there is a need to develop an alternative VOC free aqueous delivery system for SATs that provide good flow, leveling, film build and gloss in latex paints.
According to the present invention there is provided a thermoplastic polymer in fine particulate form, having at least about 20% lower bulk density than the same particle size polymer obtained by grinding. The polymer is a water-soluble, synthetic or semisynthetic associative thickener having a particle size that passes through a U.S. 20 mesh screen. The polymer can be selected from the group consisting of hydrophobically modified polyether-polyurethanes, hydrophobically modified polyether-polyurethanes bearing terminal hydrophilic groups, hydrophobically modified polyacrylates, hydrophobically modified polyether-polyols, hydrophobically modified polyacrylamide, hydrophobically modified polyvinyl alcohol and copolymers thereof, hydrophobically modified aminoplast-polyethers, hydrophobically modified hydroxyethyl cellulose, hydrophobically modified hydroxypropylcellulose, hydrophobically modified hydroxypropylmethylcellulose, hydrophobically modified ethylhydroxyethylcellulose and hydrophobically modified poly(acetal- or ketal-polyethers) comprising a backbone of poly(acetal- or ketal-polyether) which has ends that are capped with hydrophobic groups independently selected from the group consisting of alkyl, aryl, arylalkyl, alkenyl, arylalkenyl, cycloaliphatic, perfluoroalkyl, carbosilyl, polycyclyl, and complex dendritic groups wherein the alkyl, alkenyl, perfluoralkyl, and carbosilyl hydrophobic groups comprise 1 to 40 carbons, and the aryl, arylalkyl, arylalkenyl, cycloaliphatic and polycyclyl hydrophobic groups comprise 3 to 40 carbons.
The present invention provides processes for preparing fine particle size thermoplastic polymers having reduced bulk density by dissolving the polymer and rapidly insolubilizing the polymer from the solution.
According to the present invention there are further provided processes for using the polymer of the present invention in applications where reduced bulk density particulate polymer is desired, e.g., in aqueous fluid suspensions and in thickening aqueous systems such as latex paints, sizing systems, adhesives, cosmetics, pharmaceuticals, paper coatings, etc.
It has surprisingly been found that very fine particles of thermoplastic polymers, such as polyalkylene oxide based SATs having lower bulk density than the SAT particles of the same particle size obtained by grinding solid SATs can be made by dissolving them in an organic solvent at elevated temperatures and allowing the solvent to evaporate from the SAT solution. The SAT particles with lower bulk density are suitable for making stable aqueous dispersions containing 20% by weight and greater of SATs in the presence of appropriate amounts of dissolved salts. When diluted with water, these polymeric aqueous dispersions dissolve rapidly without lumping.
It was also unexpectedly found that when these SATs are suspended in a salt solution and the SAT suspension is used to thicken latex paints, the amount of SAT required to thicken the latex paint was significantly less than when the SAT was delivered as a solution in 1:4 (weight basis) butyl carbitol/water mixture.
The thermoplastic polymers can be water-soluble synthetic or semi-synthetic associative thickeners (SATs and SSATs), poly(2-ethyl-2-oxazoline), GANTREZ(copyright) poly(vinyl methyl ether-co-maleic anhydride) (available from ISP Technologies, Inc.), PEMULEN(copyright) hydrophobically modified polyacrylate (available from B. F. Goodrich), KLUCEL(copyright) hydroxypropylcellulose (available from Hercules Incorporated) (polyethylene oxide, polypropylene oxide, poly(ethylene oxide-co-propylene oxide), poly(vinylpyrrolidone), poly(vinyl acetate-co-vinyl alcohol). The synthetic or semi-synthetic associative thickeners suitable for use in the present invention could be selected from the group consisting of hydrophobically modified polyether-polyurethanes, hydrophobically modified polyether-polyurethanes bearing terminal hydrophillic groups, hydrophobically modified polyacrylates, hydrophobically modified polyether-polyols, hydrophobically modified polyacrylamide, hydrophobically modified poly(vinyl alcohol) and copolymers thereof, hydrophobically modified aminoplast-polyethers, hydrophobically modified hydroxyethylcellulose, hydroxypropylcellulose, hydrophobically modified ethylhydroxyethyl cellulose and hydrophobically modified poly(acetal- or ketal-polyethers) comprising a backbone of poly(acetal- or ketal-polyether) which has ends that are capped with hydrophobic groups independently selected from the group consisting of alkyl, aryl, arylalkyl, alkenyl, arylalkenyl, cycloaliphatic, perfluoroalkyl, carbosilyl, polycyclyl, and complex dendritic groups wherein the alkyl, alkenyl, perfluoralkyl, and carbosilyl hydrophobic groups comprise 1 to 40 carbons, and the aryl, arylalkyl, arylalkenyl, cycloaliphatic and polycyclyl hydrophobic groups comprise 3 to 40 carbons.
Compositions and processes for making such hydrophobically modified synthetic water-soluble polymers are disclosed in U.S. Pat. Nos. 4,079,028, 4,155,892, 4,496,708, 4,426,485, 4,499,233 and 5,023,309 (hydrophobically modified polyether-polyurethanes), U.S. Pat. Nos. 4,288,639, 4,354,956, 4,904,466 (hydrophobically modified polyether-polyols), U.S. Pat. No. 4,304,902 (copolymers of ethylene oxide and long chain epoxyalkane), U.S. Pat. No. 5,574,127 (hydrophobically modified polyacetal-polyethers), PCT International WO 96/40820 (hydrophobically modified polyether-polyurethanes bearing terminal hydrophilic groups), hydrophobically modified polyacetal-polyethers (U.S. Pat. No. 5,574,127), hydrophobically modified alkali-soluble emulsions (U.S. Pat. Nos. 4,514,552, 4,421,902, 4,423,199, 4,429,097, 4,663,385, 4,008,202, 4,384,096, 5,342,883 and references cited therein. For other references on hydrophobically modified alkali-soluble emulsions see, E. J. Schaller and P. R. Perry, in xe2x80x9cHandbook of Coatings Additivesxe2x80x9d, Ed., L. J. Calbo, Marcel Dekker, Inc., New York, Vol. 2, 1992, Chapter 4, p. 114 and G. D. Shay in xe2x80x9cPolymers in Aqueous Mediaxe2x80x9d, Ed. J. E. Glass, Advances in Chemistry Series, Vol. 223, Chapter 25, p. 480, 1989; American Chemical Society, Washington, D.C.), hydrophobically modified polyacrylamide (U.S. Pat. Nos.4,425,469, 4,432,881, 4,463,151, 4,463,152, 4,722,962), hydrophobically modified aminoplast-polyethers (PCT International WO 96/40625 and WO 96/40185).
Generally the upper limit of the weight average molecular weight of the polymer can be 2,000,000, preferably 500,000 and most preferably 100,000. The lower limit can be about 500, preferably 15,000 and most preferably about 20,000.
Preferably the hydrophobically modified poly(acetal- or ketal-polyethers) used in the present invention are those wherein the hydrophobic groups comprise alkyl and alkenyl groups having 8 to 22 carbon atoms and aryl, arylalkyl, arylalkenyl, cycloaliphatic and polycyclyl groups having 6 to 29 carbon atoms, more preferably wherein such alkyl and alkenyl groups have 12 to 18 carbon atoms and the aryl, arylalkyl, aryl alkenyl, cyloaliphatic and polycyclyl groups have 14 to 25 carbon atoms and most preferably wherein the alkyl groups have 16 carbon atoms.
The polymers of the present invention have a particle size that passes through a U.S. 20-mesh screen, preferably through a U.S. 40-mesh screen and most preferably through a U.S. 60-mesh screen.
In addition to or instead of the hydrophobically modified poly(acetal- or ketal-polyethers) discussed above hydrophobically modified polyether-polyurethanes as described in U.S. Pat. Nos. 4,155,892, 4,496,708, 4,426,485, 4,499,233, 5,023,309 and 5,281,654, and hydrophobically modified polyether-polyurethanes bearing terminal hydrophilic groups as described in PCT International WO 96/40820, and hydrophobically modified polyether-polyols as described in U.S. Pat. Nos. 4,288,639, 4,354,956 and 4,904,466, and hydrophobically modified polyacrylates as described in U.S. Pat. Nos. 4,514,552, 4,421,902, 4,423,199, 4,429,097, 4,663,385, 4,008,202, 4,384,096, and 5,342,883 and hydrophobically modified polyacrylamide as described in U.S. Pat. Nos. 4,425,469, 4,432,881, 4,463,151, 4,463,152, and 4,722,962, and hydrophobically modified aminoplast-polyethers as described in PCT International WO 96/40625 and WO 96/40185), can also be used to make the aqueous suspensions of the present invention. Hydrophobically modified polyurethane thickeners are low molecular weight polyether-polyurethane bearing hydrophobes. They are made by condensing relatively low molecular weight polyethylene glycol (molecular weight up to about 10,000) with hydrophobic diisocyanates and end-capping the resulting copolymers with hydrophobic alcohols or amines. They are characterized by having three or more hydrophobes-two of which are terminal and the remainder are internal. The hydrophobic groups are connected to the hydrophilic polyethylene oxide blocks through urethane linkages.
In another class of hydrophobically modified polyurethanes, disclosed in U.S. Pat. No. 4,327,008, the hydrophobes have branched structure. They are made by reacting polyalkylene oxides with a polyfunctional material, a diisocyanate, and water and end-capping the resulting product with a hydrophobic monofunctional active hydrogen-containing compound or a monoisocyanate.
Hydrophobically modified polyacrylates are alkali-soluble hydrophobically modified polyacrylates. They are made by copolymerizing a mixture of acrylic monomers with a small amount of a hydrophobic co-monomer.
The fine particle size reduced bulk density thermoplastic polymers of the present invention can be made by dissolving the polymer and rapidly insolubilizing it from the solution. This can be accomplished in a number of ways, for example:
a) Dissolve the polymer in a poor solvent at elevated temperatures and cool the solution to a temperature (ambient or below ambient temperature) at which the polymer is insoluble.
Poor solvents are those in which the polymer is substantially insoluble at ambient conditions (i.e. less than 1% by weight of polymer is dissolved, based on the weight of the solution). Examples of poor solvents include ethers, ketones, esters, hydrocarbon solvents, chlorinated hydrocarbon solvents, etc. Of these, ethers and hydrocarbon solvents with boiling points lower than 60xc2x0 C. are preferred from viewpoints of operation and cost and because of their ease of removal from the polymer.
b) Dissolve the polymer in a poor solvent (e.g., tetrahydrofuran) at elevated temperature and/or pressure, and add another poor solvent of different polarity (e.g., a hydrocarbon solvent, such as hexane) to the solution.
c) Dissolve the polymer in a solvent and evaporate the solvent at a pressure lower than atmospheric pressure. The evaporated solvent may be collected by condensing the solvent vapor without a cooler.
Solvents of this type have the characteristics to dissolve the polymer to the extent of at least 1% by weight of polymer, based on the weight of solution. Examples of such solvents include: ethers, ketones, esters, hydrocarbon solvents, chlorinated hydrocarbon solvents, etc. Of these, ethers and hydrocarbon solvents with boiling points lower than 60xc2x0 C. are preferred from view points of operation and cost and because of their ease of removal from polymer.
d) Dissolve the polymer in a poor solvent at ambient temperature at a pressure above atmospheric pressure and subject the solution to an environment of below atmospheric pressure and/or elevated temperature, whereby the solvent evaporates very rapidly.
e) Dissolve the polymer in a poor solvent at ambient temperature at a pressure above atmospheric pressure and cool the solution to below ambient temperature.
f) Dissolve the polymer in a solvent and subject the solution to an environment of below atmospheric pressure and/or elevated temperature, or purging with hot gas (e.g. nitrogen, helium, argon and air), whereby the solvent evaporates very rapidly.
g) Dissolve the polymer in a solvent and rapidly mix the polymer solution with a poor solvent under high shear and filter the polymer particles formed.
The preferred method is to dissolve the polymer in a poor solvent at ambient temperature at a pressure above atmospheric pressure and to subject the solution to an environment of below atmospheric pressure and/or elevated temperature whereby the solvent evaporates very rapidly.
To prepare aqueous fluid suspensions of the fine particulate reduced bulk density polymers of the present invention, organic or inorganic water-soluble salts having solubility of at least 10 wt % or higher could be used. These could be carbon containing salts, e.g. sodium or potassium salts of aliphatic or aromatic carboxylic acids. Inorganic salts, such as sodium or potassium carbonate, chloride or bromide can also be used. Preferred water-soluble salts are sodium and potassium formate and most preferred is sodium formate. The carboxylate salts can be used in combination with inorganic salts. These aqueous fluid suspensions and their process of preparation is the subject of companion application filed Oct. 17, 1997, xe2x80x9cFluidized Polymer Suspension of Hydrophobically Modified Poly(Acetal- or Ketal-Polyether), Polyurethane and Polyacrylatexe2x80x9d, by C. L. Burdick and A. C. Sau), the disclosure of which is hereby incorporated by reference.
An aqueous fluid suspension of 20-25 wt % solids of the SAT can be made, e.g., by adding the fine powder of the SAT to a strongly agitated aqueous solution of sodium formate containing xanthan gum. Preferably, a biocide is added before or after dispersing the SAT in the salt solution. The resulting polymeric aqueous suspension was pumpable/pourable and dissolved rapidly when added to a large excess of water under agitation. When incorporated into a latex paint, it efficiently viscosified the paint and provided good flow, leveling, film build and gloss. The aqueous fluid suspensions were stable (no phase separation, gelation or sedimentation) after 4 weeks of storage at room temperature.
The aqueous fluid suspension of the fine particulate reduced bulk density polymers of the present invention can be used to thicken aqueous systems, such as latex paints, cementitious systems, mineral slurries, joint compounds, water-borne adhesives, inks, drilling muds in oil-well drilling, aqueous systems for oil recovery, cosmetics, pharmaceuticals, coating and sizing systems for paper and paperboards, sizing and finishing systems for textiles and as additive in the manufacture of wet laid nonwoven webs. They can be used alone or in combination with at least one other thickener selected form the group consisting of hydroxyethylcellulose, hydrophobically modified hydroxyethylcellulose, hydrophobically modified ethylhydroxyethyl cellulose, methyl hydroxypropyl cellulose, ethylhydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyurethanes, polyacrylates, polyacrylamides, guar, guar derivatives, clays and alkali-soluble polyacrylates.
The fine particulate reduced bulk density polymers of the present invention can sol be used to fabricate light weight plastic products, as a tablet binder and tablet disintegrant, as an adjuvant to control release of drugs, as a packaging material for separating solvents by selective adsorption and to make electrorheological fluids.
The following examples illustrate further the present invention which relates to the preparation of aqueous dispersion of various SATs. However, they should not be construed as the only ones limiting this invention, as other process variations are possible without departing from the spirit and scope of the invention. Unless indicated, all parts and percentages are by weight.
Procedures
Solution viscosity measurement of polymer solutionsxe2x80x94The solution viscosity of polymer solutions was measured using a Brookfield (BF) viscometer (Model DV-I) at 30 rpm at ambient temperatures. The results are reported in centipoises (cps).
Evaluation of paint propertiesxe2x80x94The thickener systemsxe2x80x94aqueous dispersions or solutionsxe2x80x94were incorporated into a UCAR(copyright) 367 vinyl-acrylic latex based interior flat paint formula (pigment volume concentration=60%) to achieve an initial viscosity of 95-100 Kreb Units (KU). The details of the vinyl-acrylic flat formulation are shown in Table 1.
Materials
Tamol(copyright) 731 A dispersant (sodium salt of polymeric carboxylic acid) available from Rohm and Haas Company.
Triton(copyright) N-101 surfactant (nonylphenoxypolyethoxyethanol nonionic surfactant) available from Union Carbide Corporation.
AMP-95 (2-amino-2-methyl-1-propanol), available from Angus Chemical Company.
Colloid 640 Antifoam, (a silica/petroleum dispersion) available from Rhxc3x4ne-Poulenc Inc.
Ti-Pure(copyright) R-931 titanium dioxide, available from E. I. DuPont de Nemours and Co.
Satintone(copyright) W calcined clay, available from Englehard Industries.
ECC#1 white calcium carbonate, available from ECC International.
UCAR(copyright) 367 vinyl-acrylic latex, available from Union Carbide Corporation.
Texanol(copyright) ester-alcohol coalescent [2,2,4-trimethyl-1,3-pentanediol mono(2-methylpropanoatel] available from Eastman Chemical Co.
Proxel(copyright) GXL biocide, (1,3-benzisothiazolin-3-one) available from ICI Americas.
Disperse to Hegman 4 to 5 and let-down at slower speed as follows.
The above base paint (230 g) was mixed with the thickener solution and appropriate amount of water (total weight of thickener and water=50 g) to adjust the Stormer viscosity of the paint to 97xc2x12 KU.
Formula Constants for the Thickened Paint
The significance and scale of various paint properties are indicated below.
a) Stormer viscosity, measured 24 hours after paint preparation, is measured by a Stormer viscometer at 200 secxe2x88x921 shear rate and expressed in Kreb Units (KUs).
b) Thickening efficiency (TE) is measured as dry wt % of the thickener needed in the paint to achieve a Stormer viscosity of 95-100 KU.
c) ICI viscosity is measured by an ICI plate and cone viscometer at 12,000 secxe2x88x921 and expressed in poise.
d) Leveling by Lenata method (measured on a scale of 0-10; 0=worst and 10=best).
e) Spatter resistance by Lenata method, mid-range bar, wet film thickness (in mils) above which sag occurs.
f) Spatter resistance by roll-out over a black panel (compared on a scale of 0-10; 0=worst and 10=best).